The present invention relates to a method of manufacturing a soft magnetic alloy for use in a magnetic head, a transformer, or a choke coil or the like, and more particularly to a method of manufacturing a Fe-base soft magnetic alloy having a high saturation magnetic flux density and excellent soft magnetic characteristics.
A soft magnetic alloy for use in a magnetic head, a transformer, or a choke coil or the like must have the following characteristics:
(1) high magnetic flux density; PA1 (2) high magnetic permeability; PA1 (3) small coercive force; PA1 (4) low magnetostriction; and PA1 (5) a thin shape which can easily be formed.
The magnetic head must have the following characteristics in order to improve the wear resistance in addition to the foregoing characteristics (1) to (5):
(6) excellent hardness.
Therefore, materials for a variety of alloy systems have been studied to satisfy the foregoing characteristics when a soft magnetic alloy or a magnetic head is manufactured. Hitherto, crystalline alloys such as sendust, permalloy and iron-silicon steel and the like have been employed for use in the foregoing purposes. Recently, a Fe-base or a Co-base amorphous alloy has been used.
Under the foregoing circumstances, the magnetic head must be adaptable to a magnetic recording medium of a type having large coercive force required to record information at a high density by employing further suitable magnetic material to form the magnetic head that exhibits excellent performance. Further, the size of the transformer and the choke coil must be further reduced to be adaptable to the trend of reducing electronic equipment by using magnetic material having further satisfactory performance.
However, sendust suffers from unsatisfactorily low saturation magnetic flux density of about 11 KG although it has excellent soft magnetic characteristics. Also permalloy encounters a problem of an unsatisfactorily low saturation magnetic flux density of about 8 KG when it is formed into an alloy structure that exhibits excellent soft magnetic characteristics. The iron-silicon steel (Fe--Si Alloy) has a problem of unsatisfactory soft magnetic characteristics although it exhibits a high saturation magnetic flux density.
As for the amorphous alloy, the Co-base alloy has an unsatisfactory saturation magnetic flux density of about 10 KG although it has excellent soft magnetic characteristics. Although the Fe-base alloy exhibits a high saturation magnetic flux density of 15 KG or higher, the attained soft magnetic characteristics are unsatisfactory. The stability of the amorphous alloy against heat is insufficient, resulting in a problem to be solved. Therefore, it is difficult to simultaneously realize the high saturation magnetic flux density and excellent soft magnetic characteristics.
An alloy for a transformer having a high saturation magnetic flux density and exhibiting a low core loss has been disclosed in U.S. Pat. No. 5,069,731, the composition of which is expressed by a general formula: EQU (Fe.sub.1-a M.sub.1a).sub.100-x-y-z-t Cu.sub.x Si.sub.y B.sub.z M.sub.2t
where M.sub.1 is Co and/or, M.sub.2 is at least one element selected from a group consisting of Nb, W, Ta, Mo, Zr, Hr and Ti, and a, x, y, z and t respectively satisfy, by atom %, 0.ltoreq.a.ltoreq.0.3, 0.1.ltoreq.x.ltoreq.3, 0.ltoreq.y.ltoreq.17, 4.ltoreq.z.ltoreq.17, 10.ltoreq.y+z.ltoreq.28 and 0.1.ltoreq.t.ltoreq.5.
At least 50% of the structure is made of fine crystalline grains and the average grain size obtained by measuring the maximum crystalline grain is 1000 .ANG. or less.
The foregoing fine crystalline alloy has been developed while making a Fe--Si--B amorphous alloy, disclosed in U.S. Pat. No. 5,160,379, as a starting material. In the Fe--Si--B alloy, elements for making the structure to be amorphous are Si and B and the content of Fe in an alloy having sufficient heat stability in terms of practical use is 70 to 80 atom %. The foregoing amorphous alloy has magnetic characteristics superior to that of the conventional Fe--Si alloy (iron-silicon alloy). The fine crystalline alloy disclosed above is a Fe--M.sub.1 --Cu--Si--B--M.sub.3 alloy made by adding Cu and M elements to a Fe--Si--B alloy, where the element M.sub.3 is at least one element selected from a group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo.
It is necessary for the alloy of the foregoing type to contain Cu because it has been said that the addition of Cu causes fluctuation to occur in the amorphous to generate fine crystalline grains and, accordingly, the structure can be made fine. It has been disclosed in the foregoing application that the omission of the addition of Cu cannot easily produce fine crystalline grains, a compound phase can easily be generated and therefore the magnetic characteristics deteriorate.
In the alloy of the foregoing system, the mutual action between Cu and Nb is able to prevent the enlargement of the crystalline grains. Therefore, it has been considered that composite addition of Nb and Cu is required because sole addition of Nb or Cu cannot prevent the enlargement of the crystalline grains. The foregoing fact has been disclosed by the inventors of the foregoing disclosure in Journal of Materials Transaction, JIM, Vol. 31, No. 4 (1990), pp. 307-314.
A fact can be understood from FIG. 20, which is a composition view, of U.S. Pat. No. 5,160,379 that the low magnetostriction cannot be obtained from the alloy of the foregoing system if Si=0. Since Si acts to reduce the magnetostriction, Si must be added to reduce the magnetostriction.
The inventors of the present invention have been developing soft magnetic material by using material of a component system which is completely different from an extremely different viewpoint. Among others, there is a Fe (Co, Ni)--Zr alloy system previously disclosed in U.S. Pat. No. 4,623,387 and 4,842,657 established while considering the conventional technologies about sendust, permalloy and iron-silicon steel.
The Fe (Co, Ni)--Zr alloy system contains Zr having excellent performance of forming amorphous added thereto and, accordingly, amorphous alloy can be formed even if the amount of the addition of Zr is reduced. Therefore, the concentration of Fe can be made about 90% or higher. Further, Hf can be used as an element for forming an amorphous alloy similar to Zr. However, the Curie temperature of the alloy of a type containing Fe at a high concentration is in the vicinity of the room temperature and, therefore, the alloy of the foregoing type is not a practical alloy as the material for the magnetic core.
The inventors of the present invention have found a fact that partial crystallization of Fe--Hf amorphous alloy by a special method enables a fine crystalline structure having an average crystalline grain size of about 10 to 20 nm and disclosed this in "CONFERENCE ON METALLIC SCIENCE AND TECHNOLOGY BUDAPEST", 1980, p.p. 217 to 221. It can be considered from the disclosed technology that fining of the structure of the Fe--M alloy can be enabled even if elements such as Cu are not added. Although the mechanism of this has not been clarified yet, fluctuation of the structure is already present in a rapidly solidified state in a case where the amorphous phase is formed and the fluctuation becomes nucleation site resulting in that a multiplicity of uniform and fine nuclei are generated.
As described above, the Fe--M (Zr, Hf) alloy system do not have excellent magnetic characteristics in an amorphous state because of their low Curie temperatures. However, consideration of a fact that the foregoing alloy can be finely crystallized without addition of the non-magnetic element resulted in that making of the Fe--M amorphous alloy to be a starting material enables a fine crystalline alloy to be obtained which contains a Fe at a concentration that is considerably higher than that of the conventional alloy and, therefore, an alloy can be expected to be obtained which has a saturation magnetic flux density which is higher than that of the conventional Fe--Si--B based fine crystalline alloy.